This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-362885, filed Dec. 21, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to an X-ray control apparatus for controlling an X-ray generator which irradiates a human body or other object under examination with X-rays as the result of a rotation anode in an X-ray tube being bombarded with a beam of electrons, and an X-ray diagnostic apparatus with the X-ray control apparatus.
The X-ray diagnostic apparatus is medical apparatus which provides fluoroscopy or X-ray photography. The X-ray diagnostic apparatus has an X-ray control apparatus, which controls an X-ray generator and is generally constructed as follows:
The X-ray control apparatus comprises a high-voltage generator and an X-ray tube which is supplied with a high output voltage of the high-voltage generator to generate X-rays. The X-ray tube has an anode that is supplied with the high voltage while being rotated at a given frequency (hereinafter referred to as the rotation anode). The reason why the anode is made rotatable is to protect it against burn due to electron beams.
The frequency at which the rotation anode is driven is switched, as required, between a low-speed frequency and a high-speed frequency in order to reduce abrasion of the bearing mechanism of the rotation anode. For instance, for higher X-ray output, the high-speed frequency is used, whereas, at the stage for preparation for X-ray photography, the low-speed frequency is used.
In general, the high voltage generator uses a commercial power frequency of 50 or 60 Hz. With 50 or 60 Hz as the low-speed frequency, the rotation anode will rotate at a low speed of 3000 or 3600 rpm. With 150 or 180 Hz three times higher than the low-speed frequency as the high-speed frequency, the rotation anode will rotate at a high speed of 9000 or 10800 rpm.
In recent years, an attempt has been made to increase the thermal capacity of the rotation anode in order to generate X-rays with more stability. An increase in the thermal capacity results in an increase in the weight of the rotation anode and consequently an increase in the time required to switch between the rotational speeds of the rotation anode.
FIG. 1 show examples of rotational characteristics of rotation anodes of X-ray tubes in conventional X-ray control apparatuses.
In FIG. 1, the curve A shows the rotational characteristic of the rotation anode of small thermal capacity (say, 140, 300 or 600 KHU) and the curve B shows the rotational characteristic of the rotation anode of large thermal capacity (say, 1500 KHU). The number of rotations (rpm) of the rotation anode is shown on the vertical axis and the time (seconds) that elapses from the time at which the rotation anode was switched from low speed to high speed is shown on the horizontal axis.
The delay involved in switching the rotational speed of the rotation anode resulting from its increased thermal capacity will be explained.
As can be seen from the curve A, in the case of the rotation anode of small capacity, the time interval that elapses from the stage of preparation for X-ray irradiation for X-ray photography at which the anode rotates at about 3000 rpm to the stage of execution of the X-ray irradiation at which the anode rotates at about 10000 rpm is one second or so. Thus, X-ray photography can be performed in a short period of time.
As can be seen from the curve B, on the other hand, in the case of the rotation anode of large capacity, the time interval is about three seconds. Thus, the time required for X-ray photography is increased, which may increase burden on an operator and patients.
To reduce abrasion of the bearing mechanism of the rotation anode, it is recommended that the time interval during which time the high-speed rotation is maintained be as short as possible.
It is therefore an object of the present invention to provide an X-ray control apparatus and X-ray diagnostic apparatus which permit diagnosis to be made without extending the time of X-ray photography and consequently without imposing excess burden on the operator and patients even with a rotation anode of large thermal capacity.
According to an aspect of the present invention there is provided an X-ray control apparatus comprising: an X-ray tube having a rotation anode built in for irradiating an object under examination with X-rays; select means for selecting the rotational speed of the rotation anode of the X-ray tube from among a low speed, a medium speed, and a high speed; and drive means for driving the rotation anode into rotation at the rotational speed selected by the select means, and wherein, for X-ray irradiation by the X-ray tube, the select means selects either the medium speed or the high speed.
According to another aspect of the present invention there is provided an X-ray diagnostic apparatus comprising: an X-ray tube having a rotation anode built in for irradiating an object under examination with X-rays; select means for selecting the rotational speed of the rotation anode of the X-ray tube from among a low speed, a medium speed, and a high speed; and drive means for driving the rotation anode into rotation at the rotational speed selected by the select means, and wherein, for X-ray irradiation by the X-ray tube, the select means selects either the medium speed or the high speed.
According to still another aspect of the present invention there is provided an X-ray diagnostic apparatus comprising: an X-ray tube having a rotation anode built in for irradiating an object under examination with X-rays; select means for selecting the rotational speed of the rotation anode of the X-ray tube from a first speed and a second speed higher than the first speed; and drive means for driving the rotation anode into rotation at the rotational speed selected by the select means, and wherein, for X-ray irradiation by the X-ray tube, the select means selects the first speed for fluoroscopy and either the first speed or the second speed for X-ray photography.
With these configurations, an X-ray control apparatus and X-ray diagnostic apparatus which permit diagnosis to be made without extending the time of X-ray photography and consequently without imposing excess burden on the operator and patients even with a rotation anode of large thermal capacity can be realized.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.